Spatial light modulators (SLMs) are devices used to control the distribution of light in an optical system. SLMs are typically configured as one or two-dimensional arrays of individually addressable optical elements, representing pixels of an image. These elements modify either the amplitude or the phase of the light distribution within the optical system.
SLMs can be divided into various types, including electro-optic, magneto-optic, liquid crystal, and deformable mirror devices. These different types may be further characterized according to whether they are suitable for amplitude or phase modulation or both.
SLMs have proved to be useful in many types of applications. Many applications involve their use in display systems, where a SLM optical- system replaces a raster scan system. Other applications include optical information processing, and electrostatic printing. SLMs and their applications are described in the patents and patent applications listed in the "Related Patents" section above, which are all assigned to the same assignee as the present invention. The background sections of those references, which are incorporated by reference herein, contain extensive discussions of SLM display systems, and especially those using spatial light modulators.
For generating grey scale images, existing SLM systems use various modulation techniques are used, such as by controlling the time during which the pixels are on or off. For producing color, separate light sources for different colors, typically red, blue, and green, are used to illuminate the SLM. For each frame, all pixels of the SLM array are addressed at once and the illumination for the SLM cycles through three colors. To produce variations in 256 color, various techniques are used, such as by modulating the length of time that each pixel element is on.
Another approach to providing color is to vary the intensity of the light sources. However, a problem with this approach is that variable sources, such as tunable lasers, are expensive. Also, if color is to be adjusted at the source, some means must exists for ensuring that the correct color reaches the correct pixel, such as by individually addressing each pixel as its color is produced. However, this increases the time required to display a complete image. In order to provide a complete image within the time constraints of the human eye to integrate separate pixels, the time for switching between colors must be very fast.
Because of the wide variety of applications of SLM display systems, a need exists for alternative methods of producing color so that each system may use the technique best suited for it.